This invention relates to waveform generators for use in radar systems, and more particularly, to a waveform generator for use with an improved radar system to generate a waveform by which compensating a received radar signal for the pulse-to-pulse change in signal delay, and the pulse-to-pulse change in phase and frequency, both of which occur when an object producing a reflected signal is moving relative to the radar platform, is achieved.
As is known in the art, coherent radar systems operate to detect a target by using the amplitude, frequency, and phase of a signal reflected by the object. In synthetic aperture radar systems (SAR), the platform on which the radar system is based may move an appreciable distance between the transmission of one radar pulse and the next. In addition, if the platform is based on a moving object (aircraft, ship or land-based vehicle), movement of the platform due to turbulence, wave motion, vehicle swaying, etc. creates another factor which must be taken into account to obtain accurate radar information. It is typical in such systems that successive pulse returns are combined when the signal is processed to form a coherent array of pulse returns. There is therefore both a time delay, a doppler frequency shift, and a phase shift between the various signal returns and these must be taken into account for proper signal processing. There are thus at least two forms of signal compensation which should be implemented in a coherent radar system to provide a high degree of system accuracy; i.e. range closure compensation, and platform motion or doppler phase and frequency compensation. In our co-pending U.S. patent application Ser. No. 07/577,147, an improved radar system to effect these compensations is described. A waveform generator for use in such a system is described herein.